This invention relates to an automatic gain control amplifier circuit for use in a receiver for an intermittent sequence of data transmission signals.
In a data transmission network, a receiver must receive data transmission signals from a plurality of transmitters in an intermittent sequence. The data transmission signals are received with different intensities or levels. When the receiver is connected to the transmitters by a solid transmission medium comprising paired cables, coaxial cables, optical cables, or the like, the intensities are dependent on distances along the transmission medium between the receiver and the respective transmitters and are scarcely variable with time. At any rate, the receiver must include an automatic gain control amplifier circuit for amplifying the respective data transmission signals into digital output signals of an optimum level common to the digital output signals.
As will later become clear as the description proceeds with reference to several figures of the accompanying drawing, the intermittent sequence of data transmission signals are supplied to the automatic gain control amplifier circuit as an intermittent sequence of digital input signals. The amplifier circuit has a variable gain which is controlled for the respective digital input signals by a gain control signal so as to give the digital output signals the optimum level. The variable gain is adjusted with an appreciably long delay as compared with the transmission rate of each data transmission signal in order to insure stable operation of the amplifier circuit.
In a conventional automatic gain control amplifier circuit, the variable gain is rendered a maximum during each pause between two adjacently successive digital input signals. Under the circumstances, an unduly long recovery time is necessary before each digital input signal is amplified to the optimum level. This reduces the transmission efficiency of the data transmission network. The unduly long recovery time is indispensable also upon undesired occurrence of a momentary interruption in a certain one of the data transmission signals as referred to, for example, in an article contributed by R. S. Kerdock et al to the Bell System Technical Journal, Vol. 57, No. 6 (July-August 1978), under the title of "Results of Atlanta Experiments," on page 1873 and elsewhere.